The overall goal of this research proposal is to regenerate bone by osteoblast transplantation using synthetic biodegradable polymers. The polymer will provide temporary scaffolding to attached osteoblasts which will subsequently secrete their own extracellular matrix to form a completely natural bone tissue. Two major research thrusts are required to develop technology for cell transplantation. The first deals with appropriate cell culture techniques, and the second addresses the scaffold material and structure. The two are closely related, and examination of one issue will influence the other. The objective of this project is to integrate the two areas and develop polymer-osteoblast constructs to create new bone tissue. The three-dimensional (3-D) culture of osteoblasts attached on poly(alpha-hydroxy ester) foam scaffolds will be attempted to investigate polymer composition and foam morphology effects on the polymer degradation and osteoblast function. Alkaline phosphatase activity, collagen synthesis, and formation of mineral deposits by cultured osteoblasts in 3-D will be used to optimize the polymer scaffold. New processing methods have been developed in the applicant laboratory to fabricate 3-D, open-cell poly(alpha-hydroxy ester) foams with reproducible pore sizes and porosities. Preliminary studies also showed that poly(alpha- hydroxy esters) provided a suitable substrate for osteoblast culture and migration. The investigative team will seek to optimize the polymer scaffold and cell seeding density in order to improve phenotypic development of cultured osteoblasts. They will then investigate the efficacy of syngeneic polymer-primary osteoblast and polymer-fresh bone marrow constructs to regenerate bone using the rat segmental long-bone defect model. New bone formation and graft consolidation to host bone will be assessed radiographically as a function of time. Light and fluorescence microscopy is intended to allow quantitative and qualitative analyses of the extent, character and dynamics of new bone formation. The mechanical properties of the grafted bones will be determined to verify restoration of the integrity of the reconstituted region under functional loads. It is suggested by the applicant that the proposed project will provide clinically valuable information regarding new cell-based strategies for bone repair and replacement. It is further speculated that it will lead to a major advance in treating skeletal defects using biocompatible and biodegradable polymers. These are becoming particularly important because of the renewed concern for the safety of non-degradable implants and the potential for disease transmission, especially AIDS, with allografts. This work is intended to furnish the technology for the development of other polymer-cell constructs for use in joint surgery, and plastic and reconstructive surgery. Finally, it will attempt to determine the potential of gene therapy with transplantation of genetically-altered bone cells for treating skeletal diseases.